1. Field of the Invention
The present invention relates to a rotor of a rotary machine having claw poles and auxiliary permanent magnets for increasing effective magnetic flux.
2. Description of the Related Art
A rotor of a vehicular alternator has a plurality of claw poles extending in the axial direction alternately from opposite sides of the rotor. Recently, increase in the output power of the alternator is demanded with increase in the electric load of vehicles. In order to meet the demand, auxiliary permanent magnets are disposed between the claw poles to reduce leakage magnetic flux of the rotor.
For example, a rotor of a rotary machine disclosed in U.S. Pat. No. 5,483,116 (which corresponds to JP-A-7-123664) has a crown-shaped resinous holder in which sixteen permanent magnets are held. The holder surrounds the claw poles zigzag and is retained by flange members disposed between the claw poles or by wedge-like cross section of the permanent magnets in engagement with the claw poles. JP-A-7-298585 discloses a rotor of a vehicular alternator which has spaces between the claw poles to accommodate permanent magnets and cooling air passages between the claw poles and the field coil. Thus, permanent magnets, which can not exhibit magnetic performance sufficient to suppress the leakage magnetic flux under high temperature, are cooled. However, this structure can not introduce sufficient cooling air to cool the permanent magnets.
U.S. Pat. No. 5,306,977 (which corresponds to JP-A-5-207716) discloses a structure of the rotor for cooling the permanent magnets. The structure is composed of a non-magnetic ring for holding the permanent magnets. Cooling air passages are formed between the ring and the permanent magnets to introduce cooling air in the radially outer direction. However, in order to cool the permanent magnets sufficiently, the size of the cooling air passage has to be increased. This increases the magnetic reluctance of the magnetic circuit and, in turn, decreases the size of the permanent magnets, resulting in decrease in the output power.